1. Field of the Invention
The present invention relates to a field programmable device and more particularly a field programmable device having test provisions for detecting faults therein causing defective operations thereof. The field programmable devices to which the present invention relate include any various types of memory cell arrays, for example, a ROM (Read Only Memory), a PROM (Programmable Read Only Memory) and a FPLA (Field Programmable Logic Array).
2. Description of the Prior Art
In general, a field programmable device, such as is illustrated in FIGS. 1 and 2, comprises a memory cell array member 1, an X-direction address inverter 2, a Y-direction address inverter 4, an X-direction decoder driver 3, a multiplexer 5, a programming circuit 7 and an output circuit 6. In the memory cell array member 1, regular memory cells 13 are connected between bit regular lines 11 and regular word lines 12 at cross points of the respectively associated regular bit lines 11 and regular word lines 12. Before forwarding this field programmable device to a user, it is necessary to test it to check for faults in the peripheral circuits, such as the X- and Y-direction address inverters 2, 4, the decoder driver 3, the programming circuit 7, the multiplexer 5 and the output circuit 6. The regular memory cells 13 in the memory cell member 1 are in their original state in which no writing-in of information has been effected, when the field programmable device including the memory array member 1 is supplied from a manufacturer to a user. Therefore, it is necessary to provide test bit lines 14, word lines 15 and test memory cells 16 adjacent to the respective group of plural bit lines 11 and plural word lines 12, for enabling the detection of faults in the peripheral circuits. The test memory cells 16 are selectively placed in a conductive or non-conductive state as a result of selectively applying predetermined data signals.
In the prior art test systems for testing field programmable devices, tests for only a limited number of types of faults in the peripheral circuits are effected, and it is impossible to carry out a wide range of tests covering various types of faults in the peripheral circuits. This prevents reliable testing of the field programmable devices.